The present invention relates to a coating method, as well as a coating apparatus, which applies a coating liquid onto a continuously moving belt-shaped support (web-shaped support), and more specifically to a coating apparatus as well as a coating method which minimizes fluctuation of lateral coating thickness.
Conventionally known as methods to apply a coating liquid onto a continuously moving belt-shaped support have been a dip coating method, a blade coating method, an air knife coating method, a wire bar coating method, a gravure coating method, a reverse coating method, a reverse roller coating method, an extrusion coating method, a slide coating method, and a curtain coating method. Further, in these coating methods, the coating has been attentively carried out while paying special attention to the size as well as the accuracy of coating apparatuses so as to obtain a uniform dried lateral thickness of the coating.
Incidentally, the coating apparatus, as described in the present invention, refers to a coater and more specifically refers to a coater which comprises a pocket which uniformly supplies a supplied coating liquid in the lateral coating direction and a slit which uniformly extrudes the coating liquid which has been supplied to said pocket. Listed as such coaters are, for example, an extrusion coater, a slide coater and a curtain coater.
Of these coating methods, in the case of the extrusion coating method, two methods have been known. One, namely, is a method in which coating is carried out while a belt-shaped support, at the initiation of coating, is supported by a back roller, and the other is one in which coating is carried out while said belt-shaped support is not supported.
In regard to the extrusion coating method in which coating is carried out while a belt-shaped support, at the initiation of coating, is supported by a back roller, many patents have been applied for coating systems as well as coating apparatuses, such as Japanese Patent Publication Open to Public Inspection Nos. 56-95363 and 50-142643 which disclose single layer coating methods, as well as Japanese Patent Publication Open to Public Inspection Nos. 45-12390 and 46-236 which disclose multilayer coating systems. In these coating methods, coating is carried out in such a manner that the gap between the coater and the belt-shaped support supported by the back roller is commonly maintained to be less than or equal to 1 mm. Further, atmospheric pressure may be reduced upstream as disclosed in U.S. Pat. No. 2,681,294.
When coating is carried out employing a belt-shaped support, as a method to minimize fluctuation of lateral coating thickness, it has heretofore been carried out to mechanically adjust the lateral gap between the coater and the belt-shaped support. Further, recently, Japanese Patent Publication Open to Public Inspection No. 8-215631 discloses a technique in which a mechanism, which adjusts the gap between the coater and the belt-shaped support, is allowed to move in the lateral direction so that said gap can be adjusted at an optional position.
In regard to the extrusion coating method in which coating is carried out while the belt-shaped support, at the initiation of coating, is not supported by the back roller, many patents have been applied for coating systems as well as coating apparatuses, such as Japanese Patent Publication Open to Public Inspection Nos. 50-138036, 55-165172, and 1-288364 which disclose single layer coating methods, as well as Japanese Patent Publication Open to Public Inspection Nos. 2-251265, 2-258862, and 5-192627 which disclose multilayer coating systems.
In these coating methods, coating is carried out in such manner that the coating liquid outlet of the coater is brought into direct contact with a moving belt-shaped support in the free span between support rollers, which do not support said moving support.
In said methods, fluctuation of the lateral coating thickness on said belt-shaped support has been minimized as follows. Heretofore, as disclosed in Japanese Patent Publication Open to Public Inspection No. 2-207866, the degree of the lateral right angle of the edge of the coating liquid outlet of the coater is enhanced. Further, as disclosed in Japanese Patent Publication Open to Public Inspection Nos. 9-141173 and 11-60006, are methods recently employed in which a pressing member, which presses a belt-shaped support in the specified direction, is installed near the extrusion coater so that even though said belt-shaped support exhibits some distortion in the lateral direction, fluctuation of coating thickness as well as non-coating is minimized.
In the prior art, no disclosure has been made for how a coater itself is designed so as to match products to be coated. Further, the desired accuracy to coat said products has also not been disclosed.
As a result, when a prepared coater results in an insufficient uniformity of lateral coating thickness upon coating a coating liquid, coating is carried out while making trial and error operations such as mechanical adjustment of the gap, as well as a survey for coating conditions so that the desired uniform thickness is achieved. However, a large and expensive equipment is required to make it possible to perform such operations. In addition, it requires difficult adjustment operations and it is difficult to accurately adjust said gap to the desired spacing. Accordingly, when coating is carried out employing a coater comprising a pocket as well as a slit, it is demanded to develop a coating apparatus as well as a coating method which minimizes fluctuation in lateral coating thickness as well as satisfies coating conditions while being independent of trial and error operations, such as mechanical adjustment of the slit distance as well as alteration of coating conditions.
From the viewpoint of the foregoing, the present invention was achieved.
An object of the present invention is to provide an optimal coating apparatus as well as an optimal coating method which matches the physical properties of a coating fluid as well as coating conditions in order to minimize fluctuation in the lateral coating thickness in coatings which employ a coater comprising a pocket as well as a slit.
Embodiments to achieve the aforesaid object of the present invention will now be described.
1. In a coating apparatus, comprising at least one set of a slit and a pocket, which applies at least one layer comprising a coating liquid having a viscosity of xcexc (in Paxc2x7s) onto a belt-shaped support (web-shaped support) at a coating rate (coating speed) of u (in mm/s) so as to obtain a pre-drying coating thickness (wet coating layer thickness) of hw (in mm), a coating apparatus wherein either slit length Ls (in mm) or slit gap h (in mm) is set so as to satisfy the relationship of:
1xc3x97104 less than 12xc3x97xcexcxc3x97Lsxc3x97hwxc3x97u/h3xe2x89xa64xc3x97105.
2. In a coating method, employing a coating apparatus, provided with at least one set of a slit having a length of Ls (in mm) and a slit having a gap of h (in mm), which applies at least one layer onto a belt-shaped support at a coating rate of u (in mm/s), a coating method wherein coating liquid viscosity xcexc (in Paxc2x7s) and pre-drying coating thickness hw (in mm) are adjusted to satisfy the relationship of:
1xc3x97104 less than 12xc3x97xcexcxc3x97Lsxc3x97hwxc3x97u/h3xe2x89xa64xc3x97105.
3. In a coating method, employing a coating apparatus, provided with at least one set of a slit having a length of Ls (in mm) and a slit having a gap of h (in mm), which applies at least one layer comprised of a coating liquid of a viscosity of xcexc (in Paxc2x7s) onto a belt-shaped support so as to obtain a pre-drying coating thickness of hw (in mm), a coating method wherein coating is carried out by adjusting the coating rate to u (in mm/s) so as to satisfy the relationship of:
1xc3x97104 less than 12xc3x97xcexcxc3x97Lsxc3x97hwxc3x97u/h3xe2x89xa64xc3x97105.
4. In a coating apparatus, which is provided with at least one set of a slit and a pocket, and employed to apply at least a single coating layer onto a belt-shaped support, a coating apparatus wherein when xcex94hdmax (in mm) represents the permissible maximum value of difference xcex94hd (in mm) between the maximum value and the minimum value of fluctuation (dispersion) of the lateral coating thickness (dried coating layer thickness) hd (in mm), and xcex94h (in mm) represents the difference between the maximum value and the minimum value of fluctuation of slit gap h (in mm), xcex94h (in mm) is set based on the magnitude of xcex94hdmax (in mm) so as to satisfy the relationship of:
xcex94hxe2x89xa6hxc3x97(xcex94hdmax/hd)/3.
5. In a coating apparatus, which is provided with at least one set of a slit and a pocket, and is employed to applies at least one coating layer onto a belt-shaped support, a coating apparatus wherein when Ls (in mm) represents the length of a slit, h (in mm) represents the gap of a slit, X (in mm) represents the farthest distance of the lateral coating from the coating liquid supply outlet section, and xcex94hdmax (in mm) represents the permissible maximum value of difference xcex94hd (in mm) between the maximum value and the minimum value of fluctuation of the lateral coating thickness hd (in mm), the relationship described below is satisfied:
(X2/R4)/(Ls/h3) less than 18xc3x97(xcex94hdmax/hd).
6. In a coating apparatus which is provided with at least one set of a slit and a pocket, and is employed to apply a coating liquid having a viscosity of xcexc (in Paxc2x7s) onto a belt-shaped support at a coating rate of u (in mm/s) so as to obtain a pre-drying coating thickness of hw (in mm), a coating apparatus wherein when Ls (in mm) represents the length of said slit, Lp (in mm) represents the length of the cross-section of said pocket along the slit length, L (in mm) represents the sum of Ls (in mm) and Lp (in mm), E (in Pa) represents the Young""s modulus of a coater member, t1 (in mm) represents the thickness of the thinnest portion of said pocket of a bar on the upstream side, t2 (in mm) represents the thickness of the thinnest portion of the pocket of the bar on the downstream side, hd (in mm) represents the coating thickness after drying, and xcex94hdmax (in mm) represents the permissible maximum value of difference xcex94hd (in mm) between the maximum value and the minimum value of fluctuation of the lateral post-drying coating thickness (dried coating layer thickness) hd (in mm), the relationship described below is satisfied:
6(t1xe2x88x923+t2xe2x88x923)xcexcxc3x97hwxc3x97uxc3x97Ls(Ls/2+Lp)L3/(h4E)xe2x89xa6xcex94hdmax/hd.
7. In a multilayer coating apparatus which is provided with at least two sets of a slit and a pocket, and is employed to apply at least two layers of coating liquid onto a belt-shaped support at a coating rate of u (in mm/s), wherein when Ls (in mm) represents the length of said slit, and Ls1, Ls2, . . . , Lsixe2x88x921, Lsi, Lsi+1 . . . , Lsn represent the length of each slit in sequential order of the layers on the upstream side; Lp (in mm) represents the length of said slit of the cross-sectional length and Lp1, Lp2, . . . , Lpixe2x88x921, Lpi, Lpi+1, . . . , Lpn represent said length of each slit in sequential order on the upstream side; L represent the sum of L and Lp and L1, L2, . . . , Lixe2x88x921, Li, Li+1 . . . , Ln represents each said sum from the upstream side; E (in Pa) represents Young""s modulus of a coater member; t (in mm) represents the thickness of the thinnest portion of said pocket section of each bar and t1, t2, t3, . . . , tixe2x88x921, ti, ti+1 . . . , tn represents the thinnest portion of said thickness in sequential order from the block upstream; xcexc (in Paxc2x7s) represents the viscosity of the coating liquid, xcexci (in Paxc2x7s) represents the viscosity in the order i coating liquid from upstream; hw (in mm) represents the pre-drying coating thickness and hwi (in mm) represents the pre-drying coating thickness of the order i coating layer from upstream; hd (in mm) represents the post-drying coating thickness and hdi (in mm) represents the post-drying coating thickness if the order i coating layer from upstream; xcex94hdmax (in mm) represents the permissible maximum value of difference between the maximum value and the minimum value of fluctuation of the post-drying coating thickness, and xcex94hdmaxi (in mm) represents said value in the order i coating layer from upstream; and a coating apparatus wherein the relationship described below is satisfied: h (in mm) represents the gap of said slit and hi (in mm) represents the gap in the order of i slit from upstream, the relationship described below is satisfied:
6(tixe2x88x923+ti+1xe2x88x923)xcexci
xc3x97hwixc3x97uxc3x97Lsi
(Lsi/2+Lpi) 
Li3/hi3xe2x88x926tixe2x88x923
xc3x97xcexcixe2x88x921xc3x97hwixe2x88x921xc3x97uxc3x97Lsixe2x88x921
(Lsixe2x88x921/2+Lpixe2x88x921)
Lixe2x88x9213/hixe2x88x9213xe2x88x926
ti+1xe2x88x923xc3x97xcexci+1xc3x97
hwi+1xc3x97uxc3x97Lsi+1(Lsi+1/2+Lpi+1)
Li+13/hi+13xe2x89xa6hi
(xcex94hdmaxi/hdi)E
8. A coating method wherein at least two coating layers are applied onto a belt-shaped support at a coating rate of u (in mm/s), employing the coating apparatus described in 7.
9. The coating apparatus, described in any one of 1. and 4. through 7., wherein the surface opposite the coating surface of a belt-shaped support at the coater section is supported by a back roller.
10. The coating method, described in any one of 2., 3., and 8., wherein the surface opposite the coated surface of a belt-shaped support at the coater section is supported by a back roller.
The inventors of the present invention diligently conducted investigations to overcome the aforesaid problems. As a result, it was discovered that when coating was carried out employing a coater comprising a pocket as well as a slit, it became difficult to assure a definite flow rate of coating liquid across the coating width, due to pressure loss of the coating liquid in the coater from the time when said coating liquid was supplied into said pocket under a definite pressure to the time when said coating liquid flowed out from the slit, as well as the distortion of the slit gap due to the pressure of the supplied coating liquid. Further, it was also discovered that when a coating liquid of high viscosity was coated, said tendency was further pronounced.
Specifically, it was found that it was difficult to stabilize the lateral coating thickness of a high viscosity coating liquid only by individually adjusting coating conditions and coater conditions, and it was critical to conduct investigations for physical properties of coating liquid to be coated, as well as coating conditions (coating thickness as well as coating rate), and in addition, to conduct investigation of the slit of the employed coater and the pocket size. In order to realize these discoveries, investigations were conducted in which the general formula of fluid dynamics in regard to the fluid resistance of the fluid which flows between two flat plates. As a result, it was discovered that the lateral coating thickness was stabilized utilizing the optimal relational expression as well as optimal coefficients for the coating liquid and the coater, whereby the present invention was achieved.
In the invention, it may be preferable that the viscosity of the coating liquid is 0.05 to 10 (Paxc2x7s), more preferably, the viscosity of the coating liquid is 0.1 to 5 (Paxc2x7s). Further, it may be preferable that a coating width of the slit is 1000 mm to 1500 mm.